Sphenacodontia is a stem-based clade of derived

synapsid Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes rep ...

s. It was defined by Amson and Laurin (2011) as "the largest clade that includes '' Haptodus baylei'', '' Haptodus garnettensis'' and ''

Sphenacodon ferox ''Sphenacodon'' (meaning "wedge point tooth") is an extinct genus of synapsid that lived from about 300 to about 280 million years ago (Ma) during the Late Carboniferous and Early Permian periods. Like the closely related ''Dimetrodon'', ''Sphena ...

'', but not '' Edaphosaurus pogonias''". They first appear during the Late Pennsylvanian (

Upper Carboniferous Upper may refer to: * Shoe upper or ''vamp'', the part of a shoe on the top of the foot * Stimulant, drugs which induce temporary improvements in either mental or physical function or both * ''Upper'', the original film title for the 2013 found fo ...

) epoch. From the end of the Carboniferous to the end of the

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Pale ...

, most of them remained large, with only some secondarily becoming small in size.

Basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...

Sphenacodontia constitute a transitional

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

ary series from early pelycosaurs to ancestral

therapsid Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented mor ...

s (which in turn were the ancestors of more advanced forms and finally the mammals). One might say that the sphenacodontians are proto-therapsids (even though there is almost a 30-million-years gap between the separation of the ancestors of therapsids from other sphenacodontians and the first appearance of therapsids in the fossil record).

Characteristics

The defining characteristics include a thickening of the

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The ...

visible on its internal surface, above the large front ( caniniform) teeth; and the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...

ry teeth being set in deep sockets. All other (sister group and more primitive) synapsid clades have teeth that are set in shallow sockets.

Classification

The following taxonomy follows Fröbisch ''et al.'' (2011), Benson (2012) and Spinder (2016) unless otherwise noted. Class Synapsida *

Eupelycosauria Eupelycosauria is a large clade of animals characterized by the unique shape of their skull, encompassing all mammals and their closest extinct relatives. They first appeared 308million years ago during the Early Pennsylvanian epoch, with the f ...

** Sphenacodontia *** †'' Haptodus'' *** †''

Hypselohaptodus ''Hypselohaptodus'' is a genus of sphenacodont synapsid from the Cisuralian of England. It contains a single species, ''Hypselohaptodus grandis'', and is known only from a single specimen, a partial left maxilla, which is hosted at the Warwick ...

'' *** Pantherapsida **** †'' Kenomagnathus'' **** †'' Tetraceratops'' **** † Palaeohatteriidae ****

Sphenacodontoidea Sphenacodontoidea is a node-based clade that is defined to include the most recent common ancestor of Sphenacodontidae and Therapsida and its descendants (including mammals). Sphenacodontoids are characterised by a number of synapomorphies conce ...

***** † Sphenacodontidae ***** Therapsida

References

* Laurin, M. and Reisz, R. R., 1997
Autapomorphies of the main clades of synapsids
-

Tree of Life Web Project The Tree of Life Web Project is an Internet project providing information about the diversity and phylogeny of life on Earth. This collaborative peer reviewed project began in 1995, and is written by biologists from around the world. The site ...

External links

Synapsida: Sphenacodontia
{{Taxonbar, from=Q930410 Extant Pennsylvanian first appearances Taxa named by Llewellyn Ivor Price Taxa named by Alfred Romer

Characteristics

Classification

See also

References

External links